The present invention is directed toward the field of direct broadcast satellites (xe2x80x9cDBSxe2x80x9d) also referred to in this application as direct-to-home (xe2x80x9cDTHxe2x80x9d) satellites. In particular, a multi-beam DBS satellite is disclosed that is capable of providing regional as well as global programming in a flexible and spectrally efficient manner. Regional programming is provided by including on-board satellite circuitry for receiving, filtering, switching, combining and formatting numerous regional uplink channels that are included within beams of programming information transmitted from geographically widespread sources on the earth. By using the satellite disclosed herein, spectrally efficient regional programming can be carried out between multiple programming sources transmitting in multiple uplink beams and multiple receivers located in areas served by multiple downlink beams. The flexibility of the present invention is provided by the satellite""s on-board switching processor that can connect any uplink signal to any downlink beam and can re-map the connectivity on-the-fly. The invention""s spectral efficiency is provided, in part, by the use of multiple beams that can reuse the same uplink and downlink carrier frequencies, or that can use differing frequencies.
Prior art DTH satellites typically have one uplink beam and one downlink beam. These satellites employ a bent-pipe architecture, i.e., they simply receive, amplify and retransmit the uplink signal back to the ground. Since there is only one uplink signal, these satellites must gather all of the programming information at a central ground site (xe2x80x9cthe central hubxe2x80x9d), where the collected programming is typically formatted into the Direct Video Broadcast (xe2x80x9cDVBxe2x80x9d) standard and transmitted up to the transparent bent-pipe satellite. Such a satellite is typically in a geo-synchronous orbit so that its single downlink beam can cover the entire United States, for example.
The DVB standard multiplexes up to six video channels on to a 27.5 Mb/s bit stream. On-board the prior art DTH satellite, the uplink bandwidth is demultiplexed into the individual bit streams and amplified using an associated traveling wave tube (xe2x80x9cTWTxe2x80x9d). The amplified bit streams are then multiplexed and beamed back to earth over the single downlink beam.
The prior art DBS satellite systems suffer from several disadvantages. First, all of the programming carried by the system must be collected and formatted on the ground at the central hub. This is undesirable because it requires each of the programming sources to transmit its programming to the central hub by a dedicated connection, typically a leased high-bandwidth telephone line, or perhaps a satellite link, both of which can be very expensive to maintain and operate. Second, the prior art systems provide no efficient method of providing regional (or local) programming. The lack of local programming is considered to be the primary reason for lower than expected market penetration rates of DTH TV broadcasts and systems. Currently, DTH satellite subscribers must purchase an external antenna or basic cable-TV subscription in order to receive local programming. The present invention eliminates the need for these extra elements, providing the first complete programming solution for the DBS market. Third, the prior art satellites did not provide on-board connectivity nor did they provide flexible re-mapping of any type of on-board switching device. Therefore, reconfiguring the system to provide programming from several local sources, or combining local and global sources was difficult and expensive to configure. Because of these problems, the prior art systems only provided a set of static global sources of information and no regional programming.
Regional programming is theoretically feasible in the prior art one-beam system by combining the regional programming with the global programming at the central hub. However, because the satellite has only one downlink beam, it would be tremendously wasteful of available bandwidth to try and provide localized programming via the prior art DBS satellites. In effect, the regional programming would be transmitted as if it were global programming, since the prior art satellite has only a single downlink beam. The spectral inefficiency in such a system is obvious, and is precisely why such prior art satellites and DTH systems do not provide regional programming. Since the audience size for the regional programming is smaller, revenues will be smaller, and therefore the satellite operators would rather use the available bandwidth of the downlink beam for global programming. Further adding to the spectral inefficiency of the one beam to one beam system is the inability to reuse carrier frequencies. Since there is only one beam of information going to and from the satellite, the concept of reusing carrier frequencies is not even an option.
Another prior art DTH satellite system is the xe2x80x9cSkyplexxe2x80x9d system set forth in Canadian publication No. 2,184,123. Skyplex is designed for a single-beam system and provides limited on-board multiplexing and formatting of up to seven single-channel per carrier (xe2x80x9cSCPCxe2x80x9d) sources sharing the bandwidth of a single uplink beam. This satellite design is able to gather video signals from geographically distributed sources, but only within a single uplink beam, not from multiple uplink beams. The satellite then multiplexes the individual channels into a multiple-channel per carrier (xe2x80x9cMCPCxe2x80x9d) DVB format for downlinking over a single downlink beam to home receivers.
Although solving in part the prior art problems associated with routing all of the programming through a central hub, the Skyplex system is limited to a one-beam system and therefore does not provide a spectrally efficient or flexible means for regional programming. It does not provide a means for receiving and transmitting information in a multi-beam system, nor does it provide for flexible frequency reuse in a multi-beam system. It does not provide a mechanism for variable mapping of signals from any source beam to any destination beam or combination of destinations. It does not provide any type of on-board switching and filtering of channels in a multi-beam system, and it is incapable of on-the-fly re-mapping. These functions are desirable in a regional programming system and are not taught by the Skyplex reference.
Therefore, there remains a need in this art for a multi-beam satellite capable of providing spectrally efficient regional programming in a flexible manner.
There remains a more particular need for such a satellite having the ability to link together different geographic sources of information uplinked directly to the satellite in different uplink beams and to format these sources into a digital standard compatible with DTH satellite systems.
There remains a further need for such a satellite having the ability to map any uplink channel of information to any downlink beam in the multi-beam satellite, and to flexibly re-map the connectivity on-the-fly, without tremendous cost or complexity.
There remains another need in this art for a DTH satellite that is capable of receiving, switching, combining and formatting both global programming and regional programming in a bandwidth efficient manner.
There remains yet another need in this art for such a satellite that is capable of receiving uplink information from the conventional central-hub station, which transmits the global programming to the satellite, as well as receiving uplink information from numerous regional stations distributed throughout the geographic areas served by the satellite.
There remains a further need for such a satellite that can extract or filter the individual channels of uplink information from the global and regional programming, switch this information onto a set of downlink beams, and format the switched downlink information into a digital TDM broadcast standard, such as the DVB format.
There remains an additional need for such a satellite that includes a switching processor and a formatting processor, the switching processor for filtering and switching the incoming uplink channels of information from the regional stations and possibly from a central station, and the formatting processor for combining the switched channels and formatting them into a downlink beam according to a predetermined digital broadcast format.
The present invention overcomes the problems noted above and satisfies the needs in this field for a multi-beam DBS satellite capable of providing spectrally efficient regional audio or video programming from geographically distributed regional programming sources that transmit directly to the satellite. More particularly, the present invention provides a novel satellite architecture, including a repeater connected between multiple uplink antennas and multiple downlink antennas. The repeater has a switching processor and a formatting processor, referred to herein collectively as the xe2x80x9cswitching formatter.xe2x80x9d The switching processor includes circuitry for filtering individual channels of information from the uplink frequency division multiplexed (xe2x80x9cFDMxe2x80x9d) beams received at the uplink antennas, and also includes circuitry for switching the channels of information to form a set of switched channels. These switched channels are then combined and routed to specific downlink beam paths within the formatting processor of the invention. The formatting processor converts the switched FDM channels of information into a combined digital TDM signal that preferably corresponds to the DVB standard. The repeater also includes an input multiplexer (xe2x80x9cIMUXxe2x80x9d) for receiving a global programming signal from a central hub station and for segmenting the FDM global bandwidth into smaller sub-bands. These sub-bands are amplified using TWTs and are then combined into a downlink FDM beam by a plurality of output multiplexers (xe2x80x9cOMUXxe2x80x9d). The switched TDM bands from the switching formatter are also amplified by TWTs and combined with the global sub-bands at the inputs of each OMUX to form the downlink beams.
According to the satellite of the present invention, spectrally efficient regional programming can be carried out by directly beaming the regional programming from geographically distributed regional stations to the multi-beam DBS satellite, which links the uplink information to numerous other geographic areas served by its downlink beam patterns. Global programming can still be provided from the central hub, as known in the prior art.
The repeater disclosed in this application enables the combination of global and regional programming in a flexible and spectrally efficient manner previously unknown to the prior art. In addition, the repeater enables intelligent routing of regional programming to appropriate downlink beams that service areas that would likely respond to the specific regional programming information. The spectral efficiency of the invention is achieved, in part, through the use of multiple beams that can share some or all of the same uplink and downlink beam width. This technique of sharing the available carrier frequencies is known as frequency reuse, and is only possible in a multi-beam configuration.
The following example demonstrates the functionality of the present invention. A sporting event is taking place between two teams that are located in cities on the west coast of the United States. During the regular season this program is most likely of interest only to viewers that are within the downlink beam(s) covering the western United Statesxe2x80x94i.e. it is a regional program. But, if this is a playoff game, or a bowl game, it may be desirable to provide national or at least super-regional coverage for the event. Prior art satellites are incapable of dealing with these varying programming situations. The present invention, by distinction, can deal with both scenarios by programming the inventive satellite to filter, switch, route, combine and format the incoming regional programming signal from the west coast location to the proper downlink beams to match the coverage requirements.
In both cases, the regional program is broadcast from a west coast regional programming station, directly to the DBS satellite, where it is combined with other sources of information, such as global programming from the central hub, or other regional programming. For the regular season game, the combined signals are then routed only to a downlink beam that is servicing the west coast, thus conserving the downlink bandwidth of the satellite. For the playoff game, the inventive satellite is reprogrammed to route and combine the regional uplink channel carrying the sporting event to all of the downlink beams in the multi-beam satellite. This example demonstrates the flexibility and spectral efficiency of the present invention.
In the preferred embodiments of the present invention set forth in this application, the switching processor utilizes analog circuitry to carry out the filtering and switching functions, and the formatting processor uses digital circuitry. In these embodiments the two processors are referred to collectively as the xe2x80x9canalog/digital switching formatter.xe2x80x9d Alternatively, but not shown in detail in the drawing figures, the analog switching processor could be constructed using digital circuitry. In this alternative all-digital embodiment, digital frequency demultiplexers are used for the filtering function and a digital switch is used for the switching function.
The present invention provides many advantages over the prior art: (1) it provides a multi-beam DTH satellite system capable of transmitting and combining global programming through a central hub station and regional programming directly through the satellite, the regional programming being transmitted from various regional programming stations distributed in numerous and dispersed geographic locations; (2) it provides a satellite repeater having conventional multi-beam satellite circuitry for transmitting the global programming and an unconventional switching formatter for filtering, switching, combining and formatting the regional programming; (3) it provides a satellite repeater that receives multiple FDMA uplink beams from various sources, extracts sub-bands (or groups of channels of information) from the FDMA uplink beams, switches the extracted channels of information, combines the switched FDMA channels, converts the FDMA signals into a TDM signal, and formats the TDM signal into the DVB standard; (4) it provides the ability to map any uplink channel from either a global hub station or from a regional programming station to any downlink beam, and provides on-the-fly re-mapping of the signals; (5) it provides for direct distribution of programming information from the regional programming stations to the DTH satellite, without having to support a costly leased line to the central hub station; (6) it provides a beam-to-beam channel switching processor that enables flexible, bandwidth-efficient and cost-effective regional connectivity from the multiple uplink beams to the multiple downlink beams; and (7) it provides a spectrally efficient implementation by providing multiple uplink and downlink beams that can re-use some or all of the same carrier frequencies.
There are just some of the many advantages provided by the present invention, described illustratively in more detail below. As will be appreciated, the invention described in the attached drawings is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments are to be regarded as exemplary in nature and not restrictive.